Ocean Acidification: An Evolving Global Issue

71% area of the earth is covered with water and around 97% of it is stored in oceans. Oceans act as a natural sink for carbon dioxide gas, absorbing 30% of CO₂ released in the atmosphere due to the burning of fossil fuels. Since industrial revolution our oceans have absorbed approximately 525 billion tons of CO₂ from the atmosphere. Presently, oceans are absorbing around 22 million tons of CO₂ per day causing drop in oceans pH level by 0.1 units. The pre-industrialization pH of the ocean water was 8.179 units which dropped to 8.1074 units in the 20^th century and at present it is 8.069 units resulting 30% more acidity in the world’s oceans. Scientists has warned that ocean acidification is rapidly progressing roughly 10 times faster than any time in the last 55 million years.

What is Ocean Acidification?

The ongoing and consistent drop of pH level of ocean water is referred as ocean acidification, which is mainly caused by uptake of carbon dioxide (CO₂) from the atmosphere. It is also called as the “evil twin of global warming” and “the other CO₂ problem”. About 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes. You are also interested in Acid Rain.

Chemistry of Ocean Acidification

The acidity of any solution is generally determined by the relative concentration of Hydrogen ions (H⁺). A higher concentration of H⁺ ions in a solution results in higher acidity and lower pH. When CO₂ is dissolved in ocean water it forms carbonic acid (H₂CO₃) and frees H⁺ which then reacts with carbonate ions (CO₃²⁻) and aragonite (the stable form of calcium carbonate) to form bicarbonate (HCO₃⁻). However, as ocean acidity increases, carbonate ion concentrations fall.

CO_2 (aq) + H₂O ⇌ H₂CO₃ ⇌ HCO₃⁻ + H⁺ ⇌ CO₃²⁻ + 2 H⁺.

Further these bicarbonate ions cause trouble for marine life, which will be discussed in other post. Refer Effects of Ocean Acidification.

Causes of Ocean Acidification

The main causes of ocean acidification are given below

v  Burning of fossil fuels such as coal, oil and gas.

v  Deforestation results in fewer trees to absorb the gas. Moreover, when plants are cut down and burnt or left to rot, the carbon that makes up their organic tissue is liberated as carbon dioxide.

v  Underwater hydrothermal vents and cold seeps are naturally acidic parts of the ocean which occurs on the sea floor and are caused by underground volcanic activity.

v  Other industrial processes such as cement manufacturing also contribute to atmospheric carbon dioxide levels.

v  In coastal areas, logging can also displace acidic soil into waterways, gradually contributing to the lowering pH in the ocean.

v  Eutrophication is also one other cause of ocean acidification which results in large plankton blooms, and when these blooms collapse and sink to the sea bed the subsequent respiration of bacteria decomposing the algae leads to a decrease in seawater oxygen and an increase in CO₂ (a decline in pH).

 

Conclusion

Ocean acidification is an emerging global problem which can’t be controlled without checking CO₂ emission and pollution in the atmosphere. Sustainable management, conservation and restoration of the ocean are urgently required. If greenhouse gases emission continues as they are doing at present then by 2050, 86 percent of the world’s ocean will be warmer and more acidic than anything in modern history.

 

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